The Influence of Prior Handling on the Effective CS-US Interval in Long-Trace Taste-Aversion Conditioning in Rats

In conditioned taste aversion (CTA), a taste, the conditioned stimulus (CS), is paired with an illness-inducing stimulus, the unconditioned stimulus (US), to produce CS-US associations at very long (hours) intervals, a result that appears to violate the law of contiguity. The specific length of the maximum effective trace interval that has been reported differs from laboratory to laboratory. Metabolic rate may be a factor that influences the effective CS-US interval. Given that prior handling has been demonstrated to decrease stress and presumably lower metabolism, we examined the effect of handling on the effective CS-US intervals of 0, 90, and 180 min. Results indicated that handling rats for 1 min daily, for 21 days, may have extended the effective CS-US interval to 90 min in contrast to rats that were not handled. This finding indicates that subtle procedural differences may help explain the variability reported for the effective CS-US interval in various CTA studies.